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Sensorimotor changes such as postural and gait instabilities can affect the functional performance of astronauts after gravitational transitions. When astronauts are trained before flight with supra-threshold noisy, stochastic vestibular stimulation (SVS), the central nervous system can be trained to reweight sensory information by using veridical information from other sensory inputs (such as vision and proprioception) for postural and gait control. This reweighting, in turn, can enhance functional performance in novel gravitational environments. However, the optimal maximum amplitude of stimulation has not yet been identified that can simulate the effect of deterioration in vestibular inputs for preflight training or for evaluating vestibular contribution in functional tests in general. Most studies have used arbitrary but fixed maximum current amplitudes from 3 to 5 mA in the mediolateral (ML) direction to disrupt balance function in both ML and anterior-posterior directions in healthy adults. The goal of this study was to determine the minimum SVS level that yields an equivalently degraded balance performance. Fourteen subjects stood on a compliant surface with their eyes closed and were instructed to maintain a stable upright stance. Measures of stability of the head, trunk, and whole body were quantified in the ML direction. Objective perceptual motion thresholds were estimated ahead of time by having subjects sit on a chair with their eyes closed and giving 1-Hz bipolar binaural sinusoidal electrical stimulation at various current amplitudes. Results from the balance task suggest that using stimulation amplitudes of 280% of motion-perceptual threshold (~2.2 mA on average) significantly degraded balance performance.

INTRODUCTION
Running-related injuries are most often single-sided and are partially attributed to lower limb movement and loading asymmetries. For example, runners with tibial stress fractures demonstrate asymmetry in loading rate. Running is a dynamic athletic event in which runners often engage in both inclined and declined running with the goal of improving conditioning. Symmetry Angle (SA) is a commonly used, robust measure of determining symmetry. The purpose of this study was to compare peak vertical ground reaction force (VGRF) symmetry using the SA during uphill, level and downhill running on an instrumented treadmill.
METHODS
Eleven healthy adults volunteered to participate in this study and running at 2.7 m/s at grades of 0°, 5.74° incline and 5.74° decline were analyzed. SA was computed using the peak VGRF values from both the limbs.
RESULTS AND DISCUSSION
No statistically significant differences in SA were observed between the three running conditions. (p=0.61) The unexpected uniformity in vertical GRF across uphill, level, and downhill running is consistent with the absence of changes in the peak magnitudes of the GRF observed previously. This suggests that neither moderate uphill or downhill running result in increases in peak GRF that may be considered injurious.
CONCLUSIONS
This was the first study that looked at kinetic symmetry using peak GRF in healthy recreational runners during the three running conditions. This study suggested that uphill and downhill running does not contribute to potential differences in interlimb symmetry and could be considered as a safe alternative to level running on a treadmill.

While the popularity of triathlon is increasing, the underlying biomechanics of the various bicycling positions and saddle types are not yet understood.

PURPOSE: To determine how bicycle rider position and saddle type (road vs. triathlon) affect the bicycle-rider interface forces (BRIFs) at a standardized power and cadence. METHODS: A stationary cycling ergometer was modified to include force transducers at the saddle, bottom bracket, and stem. Anatomical measurements were made in order to fine-tune rider fit on the ergometer. 9 subjects completed riding trials in all combinations of road position, road saddle, triathlon position, and triathlon saddle. Riding trials were 6 minutes, at a standardized power output of 2 Watts per kilogram (W/kg) and 90 Revolutions per Minute (RPM). RESULTS: Analysis was broken into three categories: Road Saddle, Road Position (RR) vs. Triathlon Saddle, Road Position (TR), Road Saddle, Triathlon Position (RT) vs. Triathlon Saddle, Triathlon Position (TT), and Road Saddle, Road Position vs. Triathlon Saddle, Triathlon Position. Surprisingly, there were no significant differences in saddle vertical forces between either body positions or saddle type. However, there were significant differences at the handlebar; 8.4% more body weight supported at the handlebar in the triathlon position compared to the road position while using a triathlon saddle. CONCLUSION: Across cycling positions, there is a significant change in saddle and stem vertical forces. However, within a cycling position, saddle type does not change the amount of vertical force seen at the saddle.

A period of incoordination and fatigue is commonly associated with the transition run in triathletes, in which running mechanics are thought to be altered. Few studies have examined the changes in ground reaction forces and vertical loading rate during the transition run. Our purpose was to assess the changes that occur in ground reaction forces during a fatigued transition run in triathletes. 13 recreational male triathletes (34 ± 4.2 years) performed an incremental cycling test and a cycle to run transition on separate testing sessions. A 15-camera Vicon motion capture system collecting at 200 Hz and an AMTI force instrumented treadmill collecting at 2000 Hz were used in conjunction with a modified Plug-In Gait marker to collect trajectory and analog data for pre and post-cycling running trials. Ground reaction forces and temporal spatial parameters were assessed during stance of all running trials using Visual 3D software. Peak vertical ground reaction force and step length decreased significantly from pre-cycling to immediate post-cycling measures (p=.003, p<.001), no difference existed for either variable for pre-cycling vs. 10min post-cycling. Instantaneous peak vertical loading rate (IVLR) and step rate increased significantly from pre-cycling to immediate post-cycling measures (p=.05, p<.001), no difference existed for stride rate for pre-cycling vs. 10min post-cycling. IVLR remained significantly increased at the 10 min post-cyling (p=.035). The study findings suggest that fatigue from prolonged cycling can negatively impact triathletes’ ability to attenuate ground reaction forces in subsequent running.

Calculating and interpreting joint moments using marker position and ground reaction force (GRF) data is a fundamental part of gait biomechanics research. Due to noise in marker positions, these data are low-pass filtered prior to performing inverse dynamics. Traditionally, kinematic data are filtered at low cutoff frequencies (~6 Hz) and kinetic data are filtered at high frequencies (~30-100 Hz). This technique can result in joint moment impact peaks, particularly during high-impact movements. Filtering marker and GRF data at the same cutoff frequency has been suggested to attenuate these impact artefacts. The effect of various filtering approaches on joint moments in walking is unknown. The purpose of this study was to compare the effect of low-pass filtering cutoff frequencies on joint moments during walking. We hypothesized that filtering would not affect peak joint moments during walking due to smaller violations of the rigid body assumption compared to high-impact movements. Kinetic and kinematic data were collected for twenty-four health adults walking at self-selected speed. Marker position and GRF were smoothed using a 4th-order dual-pass Butterworth filter with cutoff frequencies of 6/45 Hz, 6/6 Hz, 10/10 Hz, for markers and GRF, respectively. A one-way repeated measures ANOVA tested for the effect of filter frequency on peak hip and knee joint moments. Peak hip and knee moments were greater when filtered at 10/10 Hz compared to 6/45 Hz. Although there were differences between cutoff frequency conditions, the effect sizes were small, suggesting that the differences are not large enough to have a meaningful effect.

Previous research has shown the utility of vibrotactile feedback to improve postural sway characteristics in persons with vestibular deficits. Tactile feedback given through vibration has been used more as a modality of training but immediate effects on postural control among older adults have not been investigated.
PURPOSE: To compare the immediate effects of tactile vibration on postural sway in healthy older adults in challenging stance and sensory conditions. METHODS: 10 healthy older adults (76.4 ± 6.8years), performed five standing balance conditions on a AMTI forceplate for 30s each: feet together on firm surface eyes open (C1), eyes closed (C2); feet together on foam surface eyes open (C3), eyes closed (C4), and tandem stance on firm surface eyes open (C5). Participants did 2 trials of each condition both with and without vibrotactile feedback. The feedback was given using a waist belt with sensors that were activated when participants swayed in a particular direction as detected by an Xbox Kinect camera (Sensory Kinetics system; Engineering Acoustics, Casselberry, FL). Center of pressure sway area was compared within each condition using a paired samples t-test to estimate the effect of vibration. RESULTS: See Table 1. Since only 5 subjects could complete C4 data was not included in statistical analysis. CONCLUSION: Tactile vibration did not acutely effect postural sway in challenging stance conditions in healthy older adults. Long term effects of tactile vibration on postural sway in challenging stance conditions need to be investigated.

Compliant flooring is a promising intervention for reducing fall-related injuries among long-term care residents but may increase the forces required for direct care staff to perform pushing tasks. We analyzed initial and sustained hand forces required for care staff to push a wheelchair (n=14) or two floor-based lifts (traditional manual and motor-driven) (n=14), loaded with average and ninetieth percentile resident weights, over four flooring systems. Compliant subflooring increased push forces compared to concrete subflooring, especially with vinyl overlay, but pushing over a compliant subfloor with vinyl overlay did not require more force than pushing over a concrete subfloor with carpet overlay. Compared to the traditional lift, the motor-driven lift substantially reduced push forces on all flooring systems. With the motor-driven lift only, resident weight did not influence push forces. These results provide new knowledge about the effects of compliant flooring and motor-driven lifts on push forces in long term care.

The purpose of the study was to determine whether increasing trunk flexion (TF) and whole body inclination (WBI) angles influences peak knee, hip, and trunk kinematics and kinetics during running. Nineteen participants ran over ground at a self-selected speed under three postures: self-selected normal (SSN), TF, and WBI. Analyses revealed significant differences between conditions for peak knee, hip, and trunk flexion angles and peak knee and hip extension moments. Both TF and WBI postures are effective strategies for reducing peak knee extension moments during running with more load distributed to the hips. This may reduce PFJ stress and therefore aid in knee injury prevention and management. Individual preference of either altered running posture should be utilized in a clinical setting.